This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-295271, filed on Sep. 27, 2000; the entire contents of which are incorporated herein by reference.
This invention relates to an image forming method, and more particularly concerns an image forming method where an image is formed by superimposing visible toner images of a plurality of colors together on a surface of a latent image recording member with a liquid developer.
Being able to obtain high quality images comparable to that of printing (e.g. offset) thanks to extremely fine toner particles of sub-micron in diameter, being able to reduce cost for copying because sufficient image density can be obtained with a small amount of toner, and being able to accomplish energy saving because the toner can be fixed to a copy sheet at a relatively low temperature, etc. are the important advantages of the liquid process type electro-photographic recording apparatus employing a liquid developer, which cannot be realized with dry type one, so that its value has been thought better lately.
There are two methods to form a multicolor image using the electro-photography: one is that both forming a visible image on a photosensitive member and transferring the image from the photosensitive member to a recording medium are carried out separately for each color, and then every visible image of each individual color is deposited in superimposed registration with each other on the recording medium, and another is that a multicolor visible image is formed on a surface of a photosensitive member by developing each color separately and successively, and then the multicolor image is collectively transferred to the recording medium.
A method to transfer a plurality of images collectively is advantageous for forming an image with reference to process speed and accuracy of registration of colors.
In the collective transferring, exposure for forming the next visible image on the visible image of the first color formed in advance is carried out. Because toner particles of about 10 micrometers in diameter are used in the electro-photography with powdered toner, exposure light is dispersed by the toner particles which constitute the visible image of the first color. Therefore the exposure of the photosensitive member for the second color was interfered, so that it was difficult to adopt the collective transferring method as the electro-photographic system using powdered toner. On the other hand, because the liquid process type recording system utilizing liquid developer has little dispersion of light due to the liquid developer even though the liquid developer remains on the photosensitive member, it is possible to expose the surface of the photosensitive member over the visible image of the first color.
Then the inventors have tried to form an image adopting the collective transferring method as the electro-photography utilizing a liquid developer. However the problem has been confirmed that the accuracy of the visible image of the second color to the visible image of the first color deteriorates, although transparency of the visible image of the first color is so high that there is no interference to the exposure for the second color.
As mentioned above, there has been a problem that the accuracy of the image of the second color is inferior to the accuracy of the image of the first color if the collective transferring is adopted in the image forming method utilizing the liquid developer.
One object of the present invention is to provide an image forming method performing the collective transferring which enables to prevent the accuracy of the image of the second color from deteriorating.
An aspect of the present invention is a method to form a visible toner image, in which an electrostatic latent image is formed on an electrostatic latent image recording member, and the electrostatic latent image is developed with a liquid developer comprising liquid carrier and toner particles, the method comprising:
forming a first visible toner image on the surface of the electrostatic latent image recording member by providing the surface of the electrostatic latent image recording member with a first liquid developer containing liquid carrier and toner particles to develop the first electrostatic latent image,
removing the liquid carrier existing on the surface of the electrostatic latent image recording member on which the first visible toner image is formed to the extent that the liquid carrier remains by a density of 5.0xc3x9710xe2x88x925 g/cm2 to 5.0xc3x9710xe2x88x923 g/cm2,
forming a second electrostatic latent image by charging and exposing the surface of the electrostatic latent image recording member on which the first developed toner visible image with the remained liquid carrier is formed, and
forming a second visible toner image on the surface of the electrostatic latent image recording member by providing the surface of the electrostatic latent image recording member with a second liquid developer containing liquid carrier and second toner particles to develop the second electrostatic latent image.
Another aspect of the present invention comprises:
(a) forming a first color toner image on an electrostatic latent image recording member comprising a cylindrical conductive substrate and a photosensitive layer, comprising,
(a-1) charging the surface of the photosensitive layer,
(a-2) exposing on the surface of the photosensitive layer by optical scanning to form an electrostatic latent image, and
(a-3) forming the first color toner image by developing the electrostatic latent image with a liquid developer having a liquid carrier containing toner particles of the first color,
(b) removing the liquid carrier to remove excess liquid carrier from the toner image of the first color containing the liquid carrier on the electrostatic latent image recording member to the extent that the liquid carrier remains by a density of 5.0xc3x9710xe2x88x925 g/cm2 to 5.0xc3x9710xe2x88x923 g/cm2,
(c) forming a toner image of a second color on the electrostatic latent image recording member, comprising,
(c-1) charging the surface of the photosensitive layer on which the toner image of the first color is formed,
(c-2) exposing the surface of the photosensitive layer by optical scanning to form an electrostatic latent image, and
(c-3) forming the second color toner image deposited in superimposed registration with the first color toner image by developing the electrostatic latent image with a liquid developer containing toner particles of the second color, and
(d) collectively transferring the first and second color toner images to a transferring member by contacting the photosensitive layer on which the both toner images are formed to the transferring member.